Pregnancy

The question asks about which structure secretes the hormone relaxin during the later phase of pregnancy. Let's understand each option before concluding.

1. Graafian follicle: The Graafian follicle is a mature ovarian follicle that releases an egg during ovulation. It primarily secretes estrogen and does not play a significant role in producing relaxin.
2. Corpus luteum: After ovulation, the Graafian follicle transforms into the corpus luteum, which secretes hormones such as progesterone and relaxin. Relaxin, produced by the corpus luteum, helps in softening the cervix and relaxing the pelvic ligaments in preparation for childbirth during the later phase of pregnancy.
3. Foetus: The fetus does not secrete relaxin. It primarily relies on the mother's hormonal system for necessary adaptations during pregnancy.
4. Uterus: The uterus is the site of fetal development, and while it undergoes changes under the influence of various hormones, it does not secrete relaxin.

By analyzing each option, we conclude that the Corpus luteum is responsible for secreting the hormone relaxin during the later phase of pregnancy.